I think it is just like you click on the middle button
–
vodkhangJun 12 '10 at 15:00

2

This is bad design because it very easy to accidentally hit buttons on a touch interface. I have an eye injury that destroyed my depth perception so I hit the screen more often than I intend. This had made me sensitive to the problem but everyone experiences it to a lesser degree. You users will find themselves quitting accidentally a lot.
–
TechZenJun 12 '10 at 16:33

iPhone applications should never quit
programmatically because doing so
looks like a crash to the user. There
may be times, however, when external
circumstances prevent your application
from functioning as intended. The best
way to handle this is to display an
attractive screen that describes the
problem and suggests how users can
correct it. This helps users in two
ways: ■ It provides feedback that
reassures users that there’s nothing
wrong with your application ■ It puts
users in control, letting them decide
whether they want to take corrective
action and continue using your
application or press the Home button
and open a different application